Process for homopolymerizing acrylonitrile

ABSTRACT

A process for the polymerization of acrylonitrile is provided using a catalyst which contains (A) an iron source, (B) an electron donor ligand, and (C) a reducing agent, in molar ratios of (B) to (A) of about 0.3 to 10:1 and of (C) to (A) of about 3 to 50:1. Preferred catalyst components are ferric acetylacetonate, bis(diphenylphosphino)-ethane and triethylaluminum.

United States Patent 1191 Yoo [ Apr.3,1973

[54] PROCESS FOR HOMOPOLYMERIZING ACRYLONITRILE [75] Inventor: Jin SunYoo, South Holland, 111.

[73] Assignee: Atlantic Richfield Company, New

York,N.Y.

22 Filed: Jan. 12, 1970 21 Appl.No.:2,373

[52] US. Cl. ..260/88.7 R, 252/431, 260/308 DS [51] Int. Cl. ..C0813/76[58] Field of Search ..260/88.7 R, 88.7 C, 85.5 R,

[56] References Cited UNITED STATES PATENTS 3/1969 Barnford et al...260/85.5 M 4/1969 O'Brien et a1 ..260/85.5 M

3,475,395 10/1969 I-lsieh ..260/88.7 R 3,117,111 l/1964 Natta et al....

3,231,553 1/1966 Chiang 3,436,383 4/1969 OBrien et a1 ..260/88.7 R

Primary Examiner-Harry Wong, Jr. Attorney-Eugene L. Bernard, Martin J.Brown, John W. Behringer, James N. Dresser, W. Brown Morton, Jr., JohnT. Roberts and Malcolm L. Sutherland [5 7 ABSTRACT 10 Claims, NoDrawings PROCESS FOR HOMOPOLYMERIZING ACRYLONITRILE This inventionrelates to the polymerization of acrylonitrile. More particularly, theinvention relates to a process for the polymerization of acrylonitrileemploying a catalyst composition which contains an iron source, anelectron donor ligand and a reducing agent. Such catalyst compositionscan be unsupported, or they can be supported on a suitable base.

Numerous catalysts have been disclosed in the prior art as suitable forthe preparation of polymeric products of acrylonitrile.Polyacrylonitriles are used extensively in the manufacture of suchmaterials as acrylic fibers, nitrile rubber products and variousplastics. Properties of polyacrylonitrile include hardness, heat andfire resistance, solvent resistance and the ability to form orientedfibers and films. The polymerization reaction is usually initiated byredox catalysts but may also be initiated by peroxides, azo compounds,high energy radiation and strong bases. The polymers of this inventioncan be used in the manner of known polyacrylonitriles of comparablemolecular weight.

It has now been found that complexes of iron with an electron donorligand of hydrocarbon-substituted elements of Group VA of the periodictable, said elements having an atomic weight of to 83, when combinedwith a reducing agent capable of reducing ferric acetylacetonate to anoxidation state of less than 2, preferably to essentially a zero state,provide a catalyst composition having highly desirable physical andchemical characteristics and, particularly, excellent catalytic activityand selectivity for the polymerization of acrylonitrile. To obtain suchcompositions, the catalyst-forming reactants are combined in a molarratio of electron donor ligand to iron of about 0.3 to 10 or more to 1,preferably about 0.7 to 2:1, and a reducing agent to iron molar ratio ofabout 3 to 50 or more to 1, preferably about 4 to 40:1.

In the preparation of the catalyst composition of the present invention,the iron source can be provided by compounds of the metal which are atleast slightly soluble in some solvent wherein the iron-Group VA ligandcomplex can be formed. Referred are the weak field ligand complexes, theligands of which readily serve in solution as transfer agents. Suitablesources of the iron can include, for example, halides, e.g. FeCl FeBrFel hydrocarbyloxy ferric diacetates, i.e., (RO)Fe(C l-l where Rrepresents alkyl, aryl, aralkyl and the like groups; phosphinecomplexes, e.g. Fe[(C H PC H,P(C H5)2]X3, where X is a halide. Alsoavailable as iron sources are chelates formed by the iron and weak fieldligands, such as B- diketones or B -keto-carboxylic acid esters andsalts of carboxylic acids. Examples of these types of iron sourcesinclude 5 -diketonato-iron (Ill), acetylacetonato-iron (Ill),propylacetonato-iron (Ill), benzoylacetonat'o-iron; chelates from B-ketocarboxylic acid esters; salts of saturated monocarboxylic acids,e.g. ferric octoate, ferric stearate, ferric phenylacetate, ferricphenylpropionate, and the like; salts of corresponding unsaturatedmonocarboxylic acids, e.g. ferric acrylate, ferric vinyl acetate, andthe like; salts of unsaturated carboxylic acids, e.g. ferric adipate,and the like; salts of corresponding unsaturated carboxylic acids, e.g.ferric muconate and the like; salts of cyclic and aromatic carboxylicacids, e.g., ferric cyclohexane carboxylate, ferric benzoate, ferricphthalates, and the like; and alkoxycarboxylates, e.g. ferricmethoxyacetate and the like. In addition the corresponding ferrous saltscan be employed. Preferred as a source of iron is ferricacetylacetonate.

The electron donor ligand component employed in preparing the ironcomplex component of the catalyst of the present invention is preferablya multifunctional organophosphine, typically either abis(diphenylphosphino)alkane or alkene. Multifunctional phosphines whichcan be employed include those having such structures as R P(CH ),,PR RPCH=CHPR and R P(CH2),.OCH PRZ where R is a hydrocarbon radical, e.g.,alkyl, aryl, alkaryl, aralkyl and cycloalkyl of from one to about 20carbon atoms, preferably two to about six carbon atoms, and can besubstituted with nondeleterious groups and n=l, 2, 3 or 4. Preferably Ris devoid of olefinic or acetylenic unsaturation. Examples of suchcompounds are bis( diphenylphosphino )ethane, bis(diphenylphosphino)propane and bis(diphenylphosphino)ethylene.Alternatively, a triorganophosphine corresponding to the general formulaR can be employed, wherein R is a hydrocarbon radical as described abovefor multifunctional phosphines; different R groups may, of course, bepresent in the same phosphine molecule. When the phosphine componentcontains aromatic groups it is generally preferred that these havemono-cyclic structures, e.g., that the groups be selected from phenyl,alkylphenyl, or phenylalkyl radicals. Triphenylphosphine is an exampleof such an aromatic phosphine component which can be employed in thecatalyst composition of this invention.

Phosphines may also be replaced by other electron donor ligands such as,for example, alkyl, aryl, alkaryl, aralkyl, or cycloalkyl phosphites,arsines, stibines or bismuthines. Other monodentate or bidentate ligandscontaining nitrogen donating centers such as 2,2- bipyridyl,ethylenediamine, 1,10-phenanthroline, 8- aminoquinone or a Schiff baseligand may also be utilized. Other electron donor ligands which can beemployed include ligands containing both phosphine and amine functionalgroups such as diethylaminoethyl diphenylphosphine, bis(diethylaminoethyl)phenylphosphine and bis(diphenylphosphinoethyl)ethylamine; ligands containing nitrogen or phosphorous and an olefinicdouble bond, such as 2-alkylphenyldiphenylphosphine,2-propenylphenyldiphenylphosphine and the like; cyclic polyenes such as1,5-cyclooctadiene, cyclooctatetraene and cyclopentadiene; anddiphosphine oxides.

The reducing agent is supplied by a compound which is capable ofreducing ferric acetylacetonate, preferably to an oxidation state lowerthan 1 and even to zero. Examples of reducing agents which are suitablein the catalyst composition of this invention include trialkylaluminums,monoalkoxydialkylaluminums, and dialkylaluminum hydrides wherein thealkyl and alkoxy groups contain up to about six carbon atoms; Grignardreagents; ally] and alkyl tin and zinc complexes; and compounds of theformula MAlR, and MBeR wherein M is an alkali metal, e.g., sodium,lithium or potassium, and R is alkyl, for example, of two of six carbonatoms.

The relative proportions of the components of the catalyst composition,i.e., the iron, the reducing agent,

and the electron donor ligand, determine the catalytic character of thecomposition. The amount of the reducing agent, e.g. triethylaluminum,can preferably vary in more or less direct proportion with the ratio ofelectron donor ligand-to-iron, generally increasing as the ligand isincreased.

The preparation of the overall catalyst composition is preferablyconducted by first forming the complex of the electron donor ligand andthe iron source and then adding the reducing agent to a solution orsuspension of that complex, in a suitable organic solvent. Suitableorganic solvents for the final catalyst composition are those which areinert to the catalyst and which will not significantly enter into, ordeleteriously affect, the eventual polymerization reaction. As specificexamples thereof may be mentioned aromatic and aliphatic hydrocarbonsand their halogenated, e.g. chlorinated, derivatives. Oxygen-containingsolvents are generally to be avoided for this purpose. The catalyst canalso be deposited on a support, such as activated carbon, etc.

Formation of the ligand-iron complex may be effected by simply mixingthe two reactants in the presence of a suitable solvent for thecomplexing reaction. The mixing may be done at room temperature or attemperatures as high as about 300F. The complex usually forms withinabout 20 to 40 minutes after mixing at elevated temperature. Suitablesolvents for the complex-forming reaction include the same solvents asthose which are suitable for use in the final catalyst composition. Ifdesired, however, the complexing may be accomplished in a solvent whichis unsuitable for use in the final composition; in this case theresultant complex will first be isolated from the reaction mixture andredissolved, or re-suspended, in a proper solvent which is inert to thefinal catalyst composition.

Thus, for example, one method of preparing a phoshine-iron complex caninvolve stirring, preferably at room temperature, a mixture ofbis(diphenylphosphino)ethane, ferric acetylacetonate and toluene. Afterthe resulting complex has been formed the reducing agent may then beadded directly to the reaction mixture.

In another method the complex may be prepared by refluxing an alcohol,e.g. ethanol, solution of the phosphine, saybis(diphenylphosphino)ethane, and ferric acetylacetonate, preferably ata temperature of about 150to 250F., and isolating the resultant complexfrom the reactant mixture. This approach'is often preferred where theiron reagent contains some water of hydration, as the water will beremoved from the complex when the latter is separated from the alcoholsolvent. The isolated complex can then be dissolved or suspended in asuitable inert solvent, e.g. toluene, and the reducing agent addedthereto to form the catalyst composition of the present invention.

The addition to the complex solution of the reducing agent is preferablyconducted in a dry, inert atmosphere, out of the presence of air, forinstance in an autoclave. Within a relatively short period of time afteradmixing of the components, e.g. about 5 to 15 minutes, an activecatalyst composition is formed which may be used to catalyze thepolymerization of acrylonitrile.

Polymerization can be effected by contacting the acrylonitrile at anelevated temperature of, for instance, about to 300F., preferably aboutto 180F., which ordinarily can be maintained by the heat of reactionwithout external heating means. A pressure of about 0 to 500 psig,preferably about 60 to 140 psig, is suitable with the catalystcomposition of the present invention. The amount of catalyst compositionused in the reaction is sufficient to effect polymerization of the feed,and often is about 0.05 to 5 weight percent, preferably about 0.1 to 1percent, of catalyst composition (not including the solvent therefor)based on the weight of acrylonitrile feed. It has also been found thatwhen the catalyst is prepared on a high surface area support, such as,for example, activated carbon, still other advantages, such as ease ofhandling, accrue.

A solid polymer product is obtained by the process of this inventionwhich is readily soluble in dimethyl sulfoxide, but insoluble in commonorganic solvents such as benzene, toluene and chlorobenzene. An averagemolecular weight of the polymeric product was determined from adimethylsulfoxide solution of the product to be in the range of about250 to 1,000 by a cryoscopic method. The degree of polymerization may becontrolled to provide a product containing primarily lower molecularweight polymers. Information obtained from spectroscopic studies was notsufficient to allow the determination of a definite structure of thepolymeric product. However, two different nitrile groups, i.e., C N andC=N, were present.

The preparation and utilization of the catalyst composition of thepresent invention are illustrated by the following example:

A 300 cc. stainless steel autoclave equipped with an air driven magneticstirrer was used as a reactor. Both 1.05 m. moles (millimoles) ferricacetylacetonate, Fe(acac) and 1.02 m. moles bis(diphenylphosphino)-ethane, rp,PC,H P, were charged to the reactor with toluene. After thereactor was purged with nitrogen for 30 minutes, a 32 percent toluenesolution of triethylaluminum (38.4 m. moles) was injected into thesystem through a serum cap. The total amount of toluene added in thereactor was 35 ml. The system was allowed to form an active catalyticspecies with vigorous stirring for about 20 minutes. Acrylonitrile (55ml., technical grade) was introduced to the catalyst solution and thereactor was tightly closed. The system was allowed to react withvigorous agitation under a pressure of 60-140 psig and a temperature ofl60-180 F. for a 3.5 hour period. A rusty brown-colored precipitate wasremoved from the autoclave together with a very small amount of liquid.The discharged reaction mixture was treated with dilute (approximately6N) hydrochloric acid to destroy the catalytic component present in theproduct. A finely powdered yellow product was separated from the mixtureand washed successively with water, then with alcohol and finally withether. The isolated product was dried overnight in a vacuum oven at F.to give a bright yellow solid in the form of a very fine powder. Thefollowing three studies of the dried sample were carried out tocharacterize the polymeric product.

Molecular Weight Determination Using a dimethylsulfoxide solution of theproduct, molecular weight was determined to be approximately 680 by acryoscopic method, indicating that about 13 monomer units per chainparticipated in the polymerization reaction. The product is readilysoluble in dimethylsulfoxide although it is insoluble or only sparinglysoluble in common organic solvents.

Infrared Spectrum An infrared spectrum of the polymeric product taken ina Nujol mull showed two strong bands at 4.4 and 5.95 microns, indicatingthe presence of C E N and C=N structures respectively. A third band at6.1 microns could be due to C=C or to C=N in a different environmentfrom that of the C=N band at 5.95 microns, or it could be due to acombination of both C=C and C=N bands. There also appeared to be NH,- OHand a carbonyl band present as well.

Proton Nuclear Magnetic Resonance Spectrum Three poorly resolved peakswere observed in the proton NMR spectrum of the product, in theapproximate ratios of 3:4:4. The first peak fell in the region common toOCH,protons found in esters. The second peak was typical of NCH, protonsand the third peak could be CH 1 protons which are alpha to a doublebonded carbon.

It is claimed:

1. A process for the preparation of polyacrylonitril by thepolymerization of acrylonitrile which comprises contacting acrylonitrilemonomer at a temperature of about 100 to 300F. with a catalystcomposition consisting essentially of the reaction product of a complexof A. a ferric compound which is at least slightly soluble in a solventemployed to form the iron-ligand complex, and

B. an electron donor ligand of a hydrocarbon-substituted phosphoruscompound having a formula of the structure:

ocn mv.

wherein R is an alkyl, aryl, alkaryl, aralkyl or cycloalkyl radical offrom one to about 20 carbon atoms and n is an integer having the valueof from 1 to 4, with C. an organic reducing agent capable of reducingferric acetylacetonate to an oxidation state of less than 2 and selectedfrom the group consisting of trialkylaluminum compounds,-monoalkoxydialkylaluminum compounds, and dialkylaluminum hydrideswherein the alkyl and alkoxy groups contain up to about six carbonatoms; Grignard reagents; allyl and alkyl tin and zinc complexes; andcompounds of the formula MAlR and MBeR wherein M is an alkali metal andR is alkyl of two to six carbon atoms; said reactants being combined ina molar ratio of B to A of about 0.3 to 10:1 and a molar ratio of C to Aof about 3 to 50:1. 2. The process of claim 1 wherein the mole ratio ofB to A is about 0.7 to 2:1 and ofC to A is about 4 to 40: l.

3. The process of claim 1 wherein C is an aluminum alkyl compound.

4. The process of claim 1 wherein B is a phosphine of the formula R P(CHPR in which R is hydrocarbon of two to about six carbon atoms and n is anumber from 1 through 4.

5. The process of claim 4 wherein the iron reactant lS

2. The process of claim 1 wherein the mole ratio of B to A is about 0.7to 2:1 and of C to A is about 4 to 40:1.
 3. The process of claim 1wherein C is an aluminum alkyl compound.
 4. The process of claim 1wherein B is a phosphine of the formula R2P(CH2)nPR2, in which R ishydrocarbon of two to about six carbon atoms and n is a number from 1through
 4. 5. The process of claim 4 wherein the iron reactant is ferricacetylacetonate.
 6. The process of claim 4 wherein B isbis(diphenylphosphino)ethane.
 7. The process of claim 4 wherein C istriethylaluminum.
 8. The process of claim 1 wherein (B) is an organophosphine.
 9. The process of claim 1 wherein (A) is ferricacetylacetonate and (B) is an organo phosphine.
 10. The process of claim1 wherein (A) is ferric acetylacetonate, (B) isbis(diphenylphosphino)ethane, and (C) is triethylaluminum.